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Tutorial blog made a nice list of places where you can find free Photoshop brushes. It is a huge list of various brush types. Take a look here.

Graphics Illustrations has some nice set of 10 brushes for free download.

Obisidian Dawn offers a lot of free Photoshop brushes for download. Brushes are good looking sorted into various categories.

R0man.de published a few series of some very nice abstract Photoshop brushes. Take a look at them here.

Pixey has published 10 cool Photoshop brushes. They are available for free download  here.